1.Field of the Invention
The present invention pertains to a gas bag inflator or generator containing a plurality of pyrotechnic grains or bodies made of a conventional gas generant or propellant formulation, preferably an azide-based composition, which bodies have a coating of an inert ignition or burn inhibitor or retardant material thereon. The inhibited generant bodies are disposed in the combustion chamber of the gas generator or inflator which produce a gas upon combustion which, after typically filtering out condensed phase products, is preferably used to inflate a gas bag which serves as a vehicle occupant restraint cushion during a collision. More particularly these generant bodies are coated with burn inhibitor materials such as a plastic resin (e.g. acrylic resin), bentonite, etc., preferably applied as a spray.
Even though the generant bodies of this invention are especially designed and suited for creating gas for inflating passive restraint vehicle crash bags as indicated, they would also be useful in other less severe inflation applications, such as aircraft slides, inflatable boats and inflatable lifesaving buoy devices where retarded or slower initial expansion is desirable.
2. Description of the Prior Art
Automobile gas bag systems have been developed to protect the occupant of a vehicle, in the event of a collision, by rapidly inflating a cushion or bag between the vehicle occupant and the interior of the vehicle. The inflated gas bag absorbs the occupant's energy to provide a gradual, controlled deceleration, and provides a cushion to distribute body loads and keep the occupant from impacting the hard surfaces of the vehicle interior.
The use of such protective gas-inflated bags to cushion vehicle occupants in crash situations is now widely known and well documented.
The requirements of a gas generant suitable for use in an automobile gas bag device are very demanding. The gas generant must have a burning rate such that the gas bag is inflated rapidly (within approximately 30 to 100 milliseconds). The burning rate must not vary with long term storage (aging) or as a result of shock and vibration during normal deployment. The burning rate must also be relatively insensitive to changes in humidity and temperature. When pressed into pellets, wafers, cylinders, discs or whatever shape, the hardness and mechanical strength of the bodies must be adequate to withstand the mechanical environment to which they may be exposed over the expected inflator system lifetime of at least ten years without any fragmentation or change of exposed surface area. Excessive breakage of the bodies could potentially lead to system failure where, for example, an undesirable high pressure condition might be created within the gas generator device, possibly resulting in rupture of the pressure housing.
The gas generant must efficiently produce relatively cool, non-toxic, non-corrosive gas which is easily filtered to remove solid and liquid combustion by-products, and thus preclude damage to the inflatable bag or to the occupant of the automobile.
The requirements as discussed in the preceding paragraphs limit the applicability of many otherwise suitable compositions, shapes and configurations thereof from being used in automotive air bag gas generators.
Both azide and non-azide based generant formulations which generate nitrogen-containing or nitrogen-rich gas to expand an inflatable occupant restraint are well known. Exemplary azide-based generants include, for example, at least one alkali or alkaline earth metal azide as the base fuel constituent. See, for example U.S. Pat. Nos. 3,741,585; 3,.895,098; 3,931,040; 4,062,708 and 4,203,787, as well as copending commonly assigned application Ser. No. 07/749,032(MI 2105-21-00) filed Aug. 23, 1991. Exemplary non-azide generants are disclosed in commonly assigned U.S. Pat. Nos. 4,931,112 and 5,015,309 as well as copending application Ser. Nos. 07/744,755(MI 1860-21-00) filed Oct. 9, 1991, and 07/787,500(MI 1859-21-00) filed Nov. 4, 1991, and additional art cited therein. Particulate ingredients of such generant compositions are typically mixed and consolidated, with or without a small amount of a suitable binder and other auxiliary ingredients, by press molding into tablets, wafers, etc., as is conventional. When the gas generant bodies are ignited and burned, nitrogen-containing gas is produced which, after filtering, is used to inflate the gas bag.
It has been proposed in U.S. Pat. Nos. 3,901,530 and 4,131,300 to form the pyrotechnic combustible material for inflators in the form of separate discs arranged side by side with inert separator means disposed between adjacent discs to facilitate quick and uniform combustion of the material as well as achieving slower inflation onset.
Inflators such as shown in commonly assigned U.S. Pat. Nos. 4,005,876; 4,296,084 and 4,547,342 contain gas generant in the form of pressed pellets or tablets (similar in shape to aspirin tablets) which are randomly packed into the inflator combustion chamber. More recently it has been proposed in commonly assigned U.S. Pat. Nos. 4,890,860 and 4,998,751 to fabricate an inflator grain by assembling a plurality of washer-shaped propellant wafers or discs in alternating relationship with a plurality of similarly shaped, meshed inert cushion members which are held in compression in the inflator combustion chamber to achieve improved performance. While such arrangements may be satisfactory for some purposes, the propellant bodies in general present a high initial surface area for burning and thus do not provide as soft of an inflation onset as is desired.
It has also been proposed to provide gas bag inflator wafers or grains with a combustion booster or enhancer coatings. See, for example, U.S. Pat. Nos. 4,200,615; 4,244,758; 4,246,051; 4,696,705; 4,698,107; 4,806,180; 4,817,828; 5,034,070 and 5,051,143. The chief purpose of these booster or enhancer coatings is to speed up, rather than inhibit or slow down, the onset of propellant combustion.
It is also known that inhibitor or restrictor, i.e. slower burning, coatings have been applied to ammunition or firearm type base propellants, as illustrated in U.S. Pat. Nos. 1,074,809; 1,308,343; 3,194,851 and 3,396,661 and solid rocket motor propellant grains, as illustrated in U.S. Pat. Nos. 3,493,446 and 5,000,885.